Smartphones made up 41 per cent of the 321.7m wireless subscribers in the US in June 2012.

The number of tablets hit 22m, according to the CTIA survey, which aggregates data from companies serving 97 per cent of wireless subscriber connections in the US.

Prepaid contracts represented 74.9m, 23.3 per cent of total mobile users, and an increase of nearly 10 per cent. The average monthly bill was $47.16, a slight decrease, despite using more data than ever before. The number of MMS messages sent increased 10.6 per cent.

More than 1.1 trillion MB of data was used from July 2011-June 2012, an increase of 104 per cent over the year.

“Americans are using more voice, data and text than ever before, but are paying less for their wireless usage than even a year ago,” said Steve Largent, President and CEO of CTIA. “With the persistent increase in usage, this survey is another proof point for why our members need more spectrum to meet consumer demands.”

According to the survey, there were 28,641 phone masts added across the country this year, totalling 285,561 nationwide. Wireless providers invested $25m (£15.6m) in capital expenditures in the last 12 months, adding more towers and upgrading networks from 3G to 4G.